Improvement in pendulum-scales



Patente-d July 28,1874.-

Fig. 3.

H. r. a G. F.- SHAW.

Pendulum-Scales.

Invenlors:

Fig. i.

UNITED STATES PATENT OFFICE.

HENRY F. SHAW AND GEORGE F. SHAW, OF BOSTON, MASSACHUSETTS.

IMPROVEMENT IN PENDULUM-SCALES.

Specification forming part of Letters Patent No. 153,460, dated July 28,1874; application filed June 1, 1874.

To all whom it may concern:

Be it known that we, HENRY F. SHAW and GEORGE F. SHAW, of Boston, Stateof Massachusetts, have invented an Improvement in Balance-Scales, ofwhich the following is a specification:

Our invention relates to balance-scales which have two curved bars orlevers, each pivoted at one end, and the one lever resting upon theother. The object of the first part of our invention is to so form thesurfaces, which bear against each. other, of the two levers of suchcurves that, while the levers shall roll and not slide upon each other,the point of contact or bearing-point shall always be in a straightline, connecting the two centers at which the levers are pivoted, andalso that said bearing-point shall pass through equal distances, whilethe indicator on one ofthe leversshall pass through equal spaces. Theobject of the second part of our invention is to hang the pan by a band,which shall pass over a segment connected with one of the 1evers, forthe purpose of maintaining a constant leverage on that side of thepivot.

Figure 1 is an elevation, and Fig. 2 a plan, of a balance scale whichillustrates our invention. Fig. 3 is to illustrate a geometricaldemonstration of the construction of the necessary curves for thelevers.

The form of scale shown is that of one to be fastened to an uprightsupport, A being the plate to be held to such support, in any suitablemanner, as by the screws a a.. B is an arm for supporting the two leversO l) and index-plate E, as shown. The lever O is pivoted at one end onthe points atb, and carries at the other end the index-finger c. Theindex-plate E is marked ott' into suitable, but equal, spaces. The leverD is pivoted on a knife-edge at e, and has an extension, f, car ryingthe segment F. Fastened to this segment, as shown, is the band g, whichsustains the pan G to contain the articles to be weighed. 'The weight Hbeing fixed rigidly on the lever C at such pointl as may be suitable inthe movementof this lever, the horizontal distance from the weight H tothe center at b varies slightly. This variation may be compensated forby slightly changing the form ot' the segment F. Instead of the fixedweight H, a

pan for carrying various weights, hung on a segment similar to F, mightbe attached to the lever C.

The manner of operation of these scales is obvious. The demonstration ofthe manner of forming the only curves to produce the effeet hereinbeforeset forth is as follows: Let K L be the centers of motion of the leversO D. We divide the straight line K L into any number of equal parts, andthrough the points of division and the centers K L we describe the arcsof circles on m m', Ste., and n n nf, 860. Having determined thedistance through which we wish the index-iinger'to pass, we divide asuitable portion of the arc m into the same number of parts, equal toeach other, as we did the line K L. It is convenient to regard thelevers in contact at the middle o of the line K L; consequently equalportions oi' the arc m, above and below K, are taken. le then drawradiuses from the points of division 1, 2, 3-12 to the center L, andthrough the points of intersection of these radiuses with the arcs, inthe order as shown, we draw the curve l? L.

It will be readily seen that a curve constructed on the principle of l?L is the only one which, swinging about end L as a center, will passthrough equal spaces on arcs described from said center,vwhile the pointof contact with line K L passes through equal spaces. The curve P L is aspiral much used in machinery when an equable rectilinear is to bederived from an equable circular motion.

The curve O K is so constructed from the curve P Lthat the levers willkeep their point of contact on the line K L, and that the levers willroll upon each other, but have no sliding contact. Supposing the pointof contact to l be at o, this will be one point for curve O K.

To obtain another point we take the distance h c' between two radiuses,and on the arc m next to, and either right or left ot', point o, andmake the distance j k equal to it, the space j k being set ott' from theradius o K on the arc a', adjacent to the arc m taken, la being thedesired point. Thus working above and below the line K L, we find pointson the arcs u n a', Ste., through which to draw the curve O K, whichpoints, supposing corresponding arcs of m m m, Ste., and n n n', Ste.,to revolve about their centers, and eross the line K L arrangedsubstantially as and for the purpose equal distances iu equal times,would be points hereinbefore set forth.

in the curve P L. 2. rlhe combination of the segment F, band It will benoticed that the line O K, which g, and levers C and D, substantially asand for is the form of the bearing-surface of lever D, the purposehereinbefore set forth.

is an ogee curve, while the line P L, which is ,Y the forni of thebearing-surface of lever C, 'l curves all in one direction.

lVe elaini as our inventioulitnesses 1. The levers C D, the nearersurface of C EDW. DUMMER,

being convex, and that of D an ogee curve, F. l). GANFIELD.

